Performance enhancement using forward error correction on powerline communication channels

The use of forward error correction (FEC) coding is investigated, to enhance communication throughput and reliability on noisy power line networks. Rate one-half self-orthogonal convolutional codes are considered. These codes are known to be effective in other environments, and can be decoded inexpensively in real-time using majority logic decoders. Extensive bit and packet error rate tests were conducted on actual, noisy in-building power line links. Coding gains of 15 dB were observed at 10^-3 decoded bit error rates. A self-orthogonal (2, 1, 6) convolutional code with interleaving to degree 7 was particularly effective, and was implemented as a VLSI microelectronic chip. Its use improved data throughput and packet error rates substantially, at data transmission rates of 9,600 bits/s     

A stator flux-oriented voltage source variable-speed drive based onDC link measurement

The authors present a new control strategy for variable speed drives, which is aimed at improving or even replacing existing volts per hertz (V/f) open loop variable-speed drives. This strategy uses only the DC link current and voltage, which are readily available in a V/f drive for protection purposes, to implement closed loop flux and torque control. Stator flux and electromagnetic torque feedback signals are derived from the DC link voltage, the DC link current, and inverter switching states. Digital implementation is seen to be possible with slight modification on existing V/f drives. Practical considerations in implementing such a system are emphasized, and experimental results are presented to show the feasibility of the scheme     

Destruction of living cells by pulsed high-voltage application

Destruction of living cells in liquid has been formed by pulsed high-voltage application to the liquid. S. cerevsaie (yeast cell) or Bacillus natto, dispersed in deionized water and one- and three-percent NaCl solution, were used in this experiment. Four different electrodes (plate-plate, needle-plate wire-cylinder, and rod-rod electrode) were tested. The survival rate of cells was measured against peak electric field E_p pulsewidth T _W, and pulse application number N. The experimental results indicate that the survivability roughly follows Weilbull distribution. Yeast cells dispersed in deionized water could be almost completely destroyed when the wire-cylinder electrode was used with E_p=20 kV/cm, T_W=100 μs, and N=200. The energy input to a unit volume of the liquid to complete the cell destruction, however, differed significantly with the electrode type. The wire-cylinder electrode required above 10-30 cal/cm ³ to destroy the yeast cell in deionized water to 10^-6 survivability. This value was less than that required more than 70 cal/cm³. Using the rod-rod electrode contained in a pressure vessel, an arc discharge was generated to produce an intensive shock wave, which also destroyed the cells by its mechanical force. In this case, 5-10 cal/cm³ of energy was required to decrease the survivability of yeast cells in deionized water to 10^-6. Though further studies are necessary, this results indicate a possibility of the cell destruction by pulsed high voltage to be used as an energy-efficient sterilization process     

A W-matrix methodology for solving sparse networkequations on multiprocessor computers

The authors describe a methodology for solving efficiently sparse network equations on multiprocessor computers. The methodology is based on the matrix inverse factors (W-matrix) approach to the direct solution phase of Ax=b systems. A partitioning scheme of the W-matrix, based on the leaf-nodes of the factorization path tree, is proposed. The methodology allows the performance of all the updating operations on vector b in parallel, within each partition, using a row-oriented processing. The approach takes advantage of the processing power of the individual processors. Performance results are presented and discussed     

On the definition of power factor and apparent power in unbalancedpolyphase circuits with sinusoidal voltage and currents

Definition for the apparent power S and for the power factor PF in unbalanced polyphase circuits with sinusoidal waveforms are presented. It is proved that the definition S²=(V_a²+V _b²+V_c²) (I _a²+I_b²+I _c²) has a definite physical meaning, leading itself to a convenient resolution in positive, negative and zero sequence, nonactive and active power. It is suggested that the power factor be represented with the help of the ratio P⁺/ S, where P⁺ is the positive sequence active powers     

A performance comparison of full- and half-bridge series resonantinverters in high-frequency high-power applications

Load-commutated full- and half-bridge series resonant inverters are dual at lower operating frequencies where the di/dt inductance L_s has negligible effect on their performance. At higher frequencies, however, the effect of inductor L_s dominates the ratings of components, and their performance is significantly different. The difference in their performance is a function of the operating frequency and is more pronounced at higher frequencies. To study the behavior of inverters at higher frequencies, a detailed analysis is presented which includes the effect of the di/dt inductance. Finally, the performance of two inverters is compared in terms of inverter kVA rating, and the kVA rating of the compensating capacitor     

Investigation of ramped air arcs near current zero in dual-flownozzle system

Ramped air arcs with a dI/dt= 6 A/μs were investigated in dual-flow nozzle system. The nozzle pressure ratio was varied to study the arc under different flow Mach number gradients. The dI/dt, dV/dt, and postzero resistance and current measurements were taken for an electrode separation of 5.5 cm and a nozzle gap spacing of 1.23 cm. The adverse shock wave effects were quantitatively observed for nozzle pressure ratios with separated flow in the nozzle. The arc power, which is equal to the total radiation losses and heat transferred from the plasma, was determined near current zero for subsonic and supersonic flow fields. It was shown that the nozzle pressure ratio is a very important parameter in the circuit breaker performance. A comparison of this work with Brown Boveri data was made. It was concluded that the convection stabilized ramped arcs near current zero are laminar and become unstable in the dielectric regime     

Electromagnetic interference from digital signal transmission onpower line carrier channels

A procedure is presented to evaluate the electromagnetic field generated by a digital transmission system on multiconductor power-line carrier channels. The vertical component of the electric field and the horizontal component of the magnetic field are defined by approximate formulaes of varying accuracy, depending on the frequency and the distance from phase conductors. Field sources are the currents traveling along the line, which are evaluated by means of an accurate simulation model of the transmission system and a rigorous wave propagation algorithm. Frequency spectra and lateral profiles of the field components are computed for single-phase and two-phase couplings on a horizontal power line. Digital channel capacity is shown to increase as the pulse repetition interval T decreases. However, if T increases, the harmonic content of the input signal code increases and, consequently, electromagnetic pollution rises for a given carrier channel. It is concluded that the EMI (electromagnetic interference) level is an important constraint which must be taken into account when choosing T and, more generally, in the design of the digital transmission system     

Basic mechanisms of generation and flow of harmonic signals inbalanced and unbalanced three-phase power systems

The basic mechanisms of generation and flow of harmonic signals in electric power networks are discussed. With regard to generation, the unbalanced operating condition of a six-pulse converter is studied. Guidelines which are applicable in the general case are obtained. With regard to flow of harmonic signals, a new relationship between distortion voltamperes and total harmonic distortion is derived. This relationship is very similar to the P/δ and Q/| V| relations which are well known in electric power flow studies     

An investigation of seated postural stability

Results of tests undertaken to identify which measures of seated posture control are most effective in two areas, distinguishing differences in the x and y direction control strategies for a given task and distinguishing differences in overall control strategies for pairs of different tasks, are presented. The test platform, calibration tests, test protocol, and data analysis method are described. The results of statistical analyses performed on the data are summarized     

Theory for finite-phase traveling-wave boundary-guided transport oftriboelectrified particles

Numerical simulations are used to picture synchronous and asynchronous domains of traveling-wave pumping of charge-conserving particles (having mass m, charge q, radius a, and mobility b) in terms of the dimensionless frequency Ω=(ω/k)/(bE₀), mass M=(m/q) (kb) (bE₀), and gravitational acceleration G=mg/qE₀, where k and ω are the wavenumber and angular frequency of the imposed wave and E₀=kV, where V is the peak voltage. The effects of having a finite number of phases consisting of discrete electrodes covered by a semi-insulating layer are highlighted. The time-average velocity in the direction of wave travel is found to be synchronous (have velocity ω/k) for 0<Ω<Ω*<1, where Ω* is reduced by having finite phases. Because the discrete electrodes result in hops of higher magnitude, they tend to result in a conversion to asynchronous hopping and `certain' modes at a lower frequency than with a sinusoidal wave. At low M, they can also result in the stalling of particle pumping as the frequency is raised. Predicted effects of image forces, dielectric layer thickness, bulk conductivity, and surface conductivity as well as particle sticking and slipping are discussed     

电力信息网络安全隔离设备的研究

政府机关或企业上网后，必须对关键的网络进行有效的信息隔离。作者介绍了专为电力实时控制网络研制的安全隔离设备，它采用双嵌入式计算机结构实现物理层的隔离。采用MAC/IP地址、协议类型及端口等的综合过滤与认证鉴别的访问控制技术，并实现了电力行业标准通信协议的应用代理，从链路层、网络层、传输层、应用层实现有效的隔离。测试证明：在提供透明的网络服务的同时，隔离设备的安全性能有极大的提高，其传输延迟和吞吐量能满足电力系统实时控制的要求。     

Distribution line communications using CSMA access control withpriority acknowledgements

The authors describe the use and performance of CSMA (carrier-sense multiple access) with priority acknowledgements for medium access control on distribution power line communication networks. Such networks suffer from highly variable, ever-changing, and unpredictable signal-to-noise ratio. The architecture of the CSMA implementation is described, along with its advantages relative to other access control schemes. The best packet length, in terms of throughput maximization, was found to approximate 1000 bits. Delay-throughput performance is measured, and the particular effects on performance of the power-line channel behavior are ascertained. Extensive tests were conducted on intrabuilding lines using channel bit rates from 1200 to 19200 bits/s, with FSK (frequency-shift keying) and spread-spectrum PSK (phase-shift keying) modems transmitting at 3 V RMS at frequencies ranging from 40 to 120 kHz. The reported results include potentially difficult cases involving transmission across power phases     

Mode ordering algorithms for sparse vector method improvement

Three node-ordering algorithms that enhance sparse vector methods without losing sparse matrix method efficiency are presented. The performance of the algorithms is compared with that of the minimum-degree algorithm for eight test systems up to 661 nodes. For the factorization of a sparse matrix into U^tU, the new algorithms give a similar or even better sparsity for U, while clearly improving the sparsity of U^-1      

Contribution to the discussion of `1987 ampacitytables-demystifying the myths'

The author discusses J. Nasilowski's remarks (see ibid., vol.26, no.4, p.605, 1990) on a paper by D.W. Zipse (see ibid., vol.25, no.5, pp.910-17, 1989). Nasilowski claimed that in M=(hS/R)^1/2, where M is the current coefficient of heating, h is the heat transfer coefficient, including both convection and radiation, S is the surface area of the conductor, and R is the resistance, M is constant for a specific material for a range of currents and for temperature rises up to about 60 K. The author argues that M is approximately constant only for a specific conductor and for restricted ranges of temperature rise and ambient temperature. In his reply, Nasilowski stresses the utility of the assumption that M =constant for calculations of steady state temperature rise of the conductors in a quiet air     

Investigation of alternative residual current compensation forimproving series compensated line distance protection

The effect of the residual compensation factor on the measuring accuracy of distance protection measurements when an earth fault occurs on a series compensated line is investigated. It is shown that, when conventional residual compensation is used, there will be an error in the impedance measurement which depends on the ratio I_sa (I_sa+K_cI_res ) where I_sa is the faulted phase current at the relaying point, K_c is the conventional residual compensation factor, and I_res is the residual current. It is also shown that this expression depends on load current and source conditions at the line ends. In consequence, errors of measurement and concomitant overreaching/underreaching can occur when conventional residual compensation methods, as applied to plain feeders, are used in series compensated applications. An alternative method of compensation has therefore been developed. This has been found to improve accuracy of measurement at the boundary and relay measurement integrity for other fault positions in series compensated line applications     

High harmonic currents in fluorescent lamp circuits

Some formulae associated with the percentage of high harmonics in the current in fluorescent lamp fixtures are derived for the cases of L and LC ballasts. The third harmonic is analyzed most carefully, and the theoretically predicted values are compared with those found experimentally. The agreement appears to be quite satisfactory. To meet the requirement of a standard, the power factor of the system, which appears to be a nontrivial point, was taken into account     

Coupled transmission lines revisited

The author presents a very satisfying and disarmingly simple way of introducing students to the parallel line coupler, which derives its S matrix directly from a knowledge of its eigenvectors and eigenvalues. For a pair of symmetrical coupled lines, the eigenvectors can be found by inspection, and the eigenvalues determined easily by means of flow graphs. The elements of the S matrix are then known, being linear combinations of the eigenvalues     

多跳中继宽带电力线通信网络中的OFDM跨层资源分配

为保障宽带电力线通信网络的有效性和可靠性,提出一种综合多跳中继宽带电力线通信网络的业务层、网络层、介质访问控制(Media Access Control,MAC)层和物理层信息的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)跨层资源分配方法.首先建立综合跨...     

Increased operating flexibility for superconducting magnetic energystorage systems through the use of self-commutation

In a superconducting magnetic energy storage (SMES) system, it is convenient to use a twelve-pulse converter as the electrical interface between the high-voltage transmission systems and the superconducting coil. The authors present a technique for the construction of a circular PQ diagram to analyze power flow for a converter and SMES. The method indicates that, if self-commutation is used, any operating state in the PQ plane may be attained. This flexibility in operating state implies that all operating conditions, from unity power factor to zero power factor lagging, are attainable in the rectifier as well as the inverter modes. The implications of this flexibility, including harmonic impact, are discussed